Plastic liquefying device

ABSTRACT

A plastic liquefying device, includes a gasifying furnace ( 19 ) for generating pyrolytic gas by heating and melting plastic waste and a liquefying tank ( 2 ) for liquefying and separating the pyrolytic gas generated in the gasifying furnace ( 19 ). The gasifying furnace ( 19 ) further comprising a heating device ( 22 ) for heating the inside of an oven-shaped furnace body ( 20 ) provided at the bottom of the furnace body ( 20 ) having a plastic waste inlet (H) provided at the top thereof and an opening and closing mechanism ( 21 ) for opening and closing the inlet (H) installed at the inlet (H). The opening and closing mechanism ( 21 ) further includes a plate shutter ( 24 ) larger than at least the opening area of the inlet (H) and a fixing device ( 25 ) for pressingly fixing the shutter ( 24 ) to the seal surface (S) around the peripheral edge part of the inlet (H). Since the inside of the furnace body ( 20 ) can be sealed by closely fitting the shutter ( 24 ) to the seal surface (S), the lowering of a pressure inside the furnace due to gas leakage and the deterioration of an ambient environment can be prevented.

TECHNICAL FIELD

[0001] The present invention relates to a plastic liquefying device for thermally decomposing plastic wastes to efficiently use the plastic wastes as reclaimed oil or the like.

BACKGROUND ART

[0002] Recently, one of the most serious issues in waste disposal problems to deal with ever-increasing wastes is how to dispose of plastic parts and plastic containers, which are utilized in a majority of industrial products such as electrical products, domestic house ware, automobiles, and PET (polyethylene telephthalate) bottles.

[0003] Since it is difficult to dispose of such plastic wastes by biodegrading (biological breakdown), which is commonly utilized to dispose of kitchen wastes, timber wastes or the like, the majority of such plastic wastes are generally incinerated. However, as is well known, when incinerating plastics, a large amount of funnel fume and poison gas are produced. Moreover, because of the high combustion temperature, there are problems such as the incinerator damage.

[0004] Therefore, recently an attempt has been made to collect these plastic wastes and recycle them as an important recycling resource. However, recycling plastic wastes entails onerous work such as collecting and separating plastic wastes by each type of plastic constituent, color, etc. As a result, the large amount of cost and labor is involved and the recycling plastic wastes does not meet its cost accounting.

[0005] The present inventors developed a novel plastic liquefying systems for efficiently disposing of the above-mentioned plastic wastes and recycling them as reclaimed oil or the like, and filed patent applications (Japanese Patent Application No. 2000-63335, etc.) for these systems.

[0006] As shown in FIG. 12, this plastic wastes liquefying device comprises mainly a gasifying furnace 1 for melting plastic wastes by way of heat from a gas burner 4, etc. and generating pyrolytic gas by thermally decomposing, and a liquefying tank 2 for liquefying the pyrolytic gas which is generated in the gasifying furnace 1 after cooling and condensing. Specifically, after thermo-plastic wastes are melted and gasified into the pyrolytic gas including stylen-monomer and low monocular gravity polyethylene through a pyrolitical decomposition process in the gasifying furnace 1. The pyrolitic gas is then contacted with cooling water to cause vapor-liquid contact, and is re-liquefied by being cooled and condensed in the liquefying tank 2. Finally, the decomposed liquid is separated from the cooling water. The decomposed gas can be used as a material or the like for a new plastic product or fuel for a boiler, so that effective use of the decomposed liquid is achieved.

[0007] As shown in the drawings, the inlet of the gasifying furnace 1 is opened, and the plastic wastes can be loaded into the gasifying furnace 1. The shutter 3 is closed. Then, the plastic wastes start melting and liquefying, and become fusion-liquid by the heat of the burner 4. A part of the fusion liquid is sequentially and pyrolytically decomposed, then gasified. The pyrolytic gas flows into a gas line G through a gas outlet 5, and reaches the liquefying tank 2. This liquefying tank 2 integrally includes a jet scrubber 7, a neutralization column 8, etc. in a water tank 6 which stores the liquid. The pyrolytic gas reached to the liquefying tank 2, is contacted with cooling water which belches up from the jet scrubber 7 having a cooling water circular line L2 to cause vapor-liquid contact, and thus is rapidly cooled, condensed and liquefied. Then, the decomposed liquid resulting from the pyrolytic gas is temporarily stored into the water tank 6 together with the cooling water.

[0008] The above-mentioned blended liquid, which consists of the decomposed liquid and the cooling water, can be separated into the decomposed liquid and water at above and below respectively by specific gravity, after a certain time has elapsed. The decomposed liquid, which is separated into the upper side of the water tank, overflows a weir 9 positioned at the end of the water tank 6 and flows into an oil line L1. After removing solids by filtering through a filter 10, reclaimed oil or the like made from decomposed oil can be collected into a recovery tank 12. The water, which is stored in the lower side of the tank, can be pumped by a pump 11 out from the water tank 6 and re-sent into the jet scrubber 7 through a cooling water circular line L2. Afterwards, the water can be re-used as cooling water for cooling the high temperature pyrolytic gas which sequentially flows in.

[0009] The pyrolytic gas which has not been liquefied by the jet scrubber 7, and detrimental constituents such as chlorine and bromine which cannot be liquefied by cooling, are sent to the neutralization column 8 in the form of gas. Then, the pyrolytic gas can be cooled and condensed again with the newly provided cooling water from a cooling water line L4, and be simultaneously neutralized by neutralizer supplied from a neutralization tank 13. The process makes the pyrolytic gas harmless, and the harmless gas is retuned to the gasifying furnace 1 via a gas recovery line G2. Thus, the pyrolytic gas can be recycled as fuel gas, combustion air, etc. for the burner 4. Also, the exhaust combustion gas which is emitted from the burner 4, flows into an exhaust gas line G1 through a jacket 16 which covers the gasifying furnace 1, and is discharged into the atmosphere after being cleaned and filtered by a filter 14. On the other hand, the superfluous cooling water which is stored in the water tank 6 of the liquefying tank 2 can be sequentially discharged through an exhaust line L3.

[0010] According to the above-described plastic liquefying device, it makes it possible to efficiently dispose of plastic wastes which were difficult to dispose of in the past. The plastic wastes can be recycled as burnable reclaimed oil, so that it promotes the economic and efficient recycling of plastic wastes. In regards to the above-mentioned process of recycling plastic wastes, it displays excellent effects such as the removal of the local area pollution, because in principal there is no possibility of any toxic gas leak. The reference numeral 15 denotes a hopper which facilitates the loading of plastic wastes into the device.

[0011] However, a few problems remain as described below, regarding the above-mentioned plastic liquefying device.

[0012] (1) After plastic wastes are loaded into the gasifying furnace 1, the inlet of the gasifying furnace 1 is completely closed by a plate shutter 3. As shown in FIG. 13A and FIG. 13B, the shutter 3 engages with rails 17 and 17 which are located at both sides of the shutter 3, and can be horizontally moved to open and close along the rails 17 and 17 by a rack-and-pinion mechanism driven by a motor 18. When the shutter 3 is closed, it is simply placed by its specific gravity on the sealing surface S of the inlet. Therefore, there would be a possibility that when the pressure in the gasifying furnace 1 is increased, the gas which is thermally decomposed may leak from the gap between the shutter 3 and the inlet, whereby the surrounding environment may be contaminated, the inner pressure may be lowered, and the amount of the thermally decomposed gas supplied may be decreased. Also, the plastic wastes and dirt may adhere to the sealing surface S of the inlet while loading the plastic wastes. Then the shutter 3 may not be closed completely, consequently leaving a gap between the shutter 3 and the inlet, and resulting in similar inconveniences.

[0013] (2) Also, if the solids (insolubles) such as dirt, metal scraps or timber are adhered to the plastic wastes which will be processed in the gasifying furnace 1, these solids may accumulated or sticked to the bottom of the gasifying furnace 1 as residua, so that not only is the capacity of the furnace decreased but also the degree of heat conductivity may drastically deteriorate, because the accumulated solid may act as a heat insulant of the bottom of the furnace.

[0014] Therefore, regular removal of this accumulated solid is necessary, but this entails manual labor. Consequently, the device needs to be turned off and must be in a deactivated condition until the inside of the gasifying furnace 1 is cooled down completely. Then, workers have to remove the solid from the inlet with a scraper, a vacuum cleaner or the like, so that the work efficiency is drastically deteriorated and also the cleaning work is burdensome.

[0015] (3) In the liquefying tank 2, the water and oil are separated by the specific gravity by way of an overflow system. For example, substances such as terephthalic acid, which is a constituent element of PET bottles, when heated, directly breaks down into condensation without liquefying, so that the substances accumulate into the bottom of water tank 6, and this makes it difficult to collect them by the specific gravity separation. Thus, there is a limit on the types of plastic that can be dealt with. In addition, when the various kinds of mixed plastics are disposed, the process needs further labor work to separate the plastics depending upon the types of plastic before the disposal.

[0016] (4) Also, when plastic wastes such as injectors and catheters from medical institutions such as hospitals and clinics which may possibly contain infectious bacterial pathogen are disposed, it is necessary for such plastic wastes to be disposed after being submitted to sterilization for a given length of time under high pressure and high temperature. However, if the plastic wastes are disposed by the above-mentioned liquefying device in the same way as the normal plastic wastes disposal, in the initial process, the infectious bacterial pathogen which is adhered to the surface of these plastic wastes, is not sterilized completely and flows into the liquefying tank 2 together with the vapor. Consequently, the infectious bacterial pathogen may possibly contaminate the inside of the device or interfuse with the reclaimed oil.

DISCLOSURE OF THE INVENTION

[0017] One aspect of the present invention concerns a plastic liquefying device, which comprises a gasifying furnace for generating pyrolytic gas by heating and melting plastic wastes and a liquefying tank for liquefying the pyrolytic gas generated in the gasifying furnace and then separated. The gasifying furnace further includes a heating means provided at the bottom of the oven-shaped furnace body having an inlet at the top thereof for heating the inside of an oven-shaped furnace body, and an opening and closing mechanism positioned at the inlet for opening and closing the inlet. The opening and closing mechanism further includes a plate shutter which is larger than at least the opening area of the inlet and a locking means for securing the shutter to the sealing surface of the peripheral edge of the inlet.

[0018] Since the inlet for the plastic wastes can be hermetically closed, the lowering of the pressure inside the furnace due to gas leakage and the deterioration of the surrounding environment can be certainly prevented.

[0019] The shutter may include a sliding means for causing the shutter to move horizontally so as to open and close the inlet. For example, the sliding means can employ hydraulic cylinders, one end of which is connected to the shutter, and the other end is pivotably connected to the furnace body. Then, it is able to quickly open and close the inlet.

[0020] If the hydraulic cylinders which secure the shutter onto the sealing surface by way of pressure is employed as the above-mentioned locking means, the shutter can be completely closed.

[0021] If a purge gas header is provided at the peripheral edge of the inlet to spray purge gas onto the sealing surface of the inlet, thereby catching dust on the sealing surface, the sealing effect is prevented from being impaired.

[0022] If the bottom part of the furnace body has a corrugated shape defined by a plurality of canaliculate members which are placed parallel to each other, the superficial area of the bottom part of the furnace is enlarged. Then, the heat conductivity from the heating means to the furnace body can be enhanced, and an efficient melting process can be also promoted.

[0023] Each end of each of canaliculate members may merge to a discharge pipe, and also the canaliculate members and the discharge pipes may respectively include screw conveyers inside themselves. Then, the solids which have not been melted and have accumulated at the bottom of the furnace are easily discharged. Accordingly, the decrease of the furnace body capacity and the deterioration of the heat transmission can be avoided.

[0024] The heating means may include a gas burner. A jacket may be provided around the furnace for guiding the exhaust gas from the gas burner, and parting strips may be positioned spirally inside the jacket. The heat from the heating means is then efficiently transmitted to the furnace body, and the efficient melting is further promoted.

[0025] Another aspect of invention concerns a plastic liquefying device, which includes a gasifying furnace for generating pyrolytic gas by heating and melting plastic wastes and a liquefying tank for liquefying the pyrolytic gas generated in the gasifying furnace and then separating the pyrolytic gas. The gasifying furnace includes a vertical tube shape furnace body to receive infectious plastic wastes, a heating means for heating the furnace body from its surroundings to generate the pyrolytic gas by pyrolytically decomposing the infectious plastic wastes, and an agitator to agitate the inside of the furnace body. The top of the furnace body includes an inlet to receive the infectious plastic wastes, a lid to open and close the inlet and a gas outlet to discharge the pyrolytic gas. The gas outlet has an opening and closing valve which automatically opens and closes.

[0026] Accordingly, the furnace body can be hermetically sealed and the inside of the furnace body can be filled with high-pressure steam, so that the sterilization or removal of infectious bacterial pathogen which has adhered to plastic wastes can be completely undertaken.

[0027] Also, the above-mentioned furnace body may be made of a pressure vessel which includes hemispheric metal end covers respectively positioned at the top and bottom of the vertical tube-shaped metallic sack body. The opening and closing lid and gas outlet may also be provided at the top of the furnace body. Consequently, the inside pressure of the furnace body can be safely increased.

[0028] In addition, the above-mentioned agitator may include a drive shaft which is located at the shaft center part of the furnace body, a driving motor which rotates the drive shaft and a plurality of moving vanes which radially extend from the drive shaft. The moving vanes may revolve in contact with the bottom of the furnace body. So, when the plastic wastes are melted, an efficient pyrolytic decomposition can be conducted by agitating the inside of the furnace, and the deterioration of the heat transmission which can be caused by the solid or the like accumulated at the bottom of the furnace can be prevented.

[0029] If the bottom of the furnace further includes an outlet to discharge insolubles, the insolubles which have accumulated at the bottom of the furnace can be easily removed by driving the agitator. Accordingly, the cleaning of the inside of the furnace does not entail a large amount of labor and time.

[0030] Still another aspect of the present invention according to the present invention concerns a plastic liquefying device which comprises a gasifying furnace for generating pyrolytic gas by simultaneously melting various types of plastic wastes, and a liquefying tank for liquefying and separating the pyrolytic gas generated in the gasifying furnace. The bottom of the gasifying furnace is narrowed like a valley shape, which further includes a screw conveyer and a discharge opening for discharging insolubles at the bottom.

[0031] With this liquefying device, it is also easy to discharge insolubles, which have not been melted and have accumulated at the bottom of the surface, by driving the screw conveyer. Therefore, the decrease of the furnace body capacity and the deterioration of the heat transmission can be avoided.

[0032] The liquefying tank which may be a landscape water tank, may include a jet scrubber, which sprays cooling water onto the pyrolytic gas and condenses the pyrolytic gas, and a cleaning column, which cleans the exhaust gas. The bottom of the water tank may be narrowed like a funnel form. The bottom part may be connected to a drain line, and the middle part of the water tank is connected to an oil recovery line, so that the oil and water are separated, and the other substances of which specific gravity holds heavier than water can be certainly separated.

[0033] In addition, the drain line may include a neutralization tank for infusing the neutralizer. Therefore, the separated water can be efficiently neutralized. Consequently, the inconveniences such as acid corrosion of the pipes or the like caused by the acid water can be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is a longitudinal sectional view, which shows an embodiment of the gasifying furnace of the present invention;

[0035]FIG. 2 is a cross-sectional view taken along the line A-A in FIG. 1;

[0036]FIG. 3 is a cross-sectional view taken along the line Y-Y in FIG. 1;

[0037]FIG. 4 is a cross-sectional view taken along the line Y-Y in FIG. 1;

[0038]FIG. 5 is an enlarged partial view of the A part in FIG. 1;

[0039]FIG. 6 is an enlarged partial view of the A part in FIG. 1;

[0040]FIG. 7 is an enlarged partial view of the A part in FIG. 3;

[0041]FIG. 8 is an enlarged partial view of the B part in FIG. 3;

[0042]FIG. 9 is an enlarged partial view of the A part in FIG. 1;

[0043]FIG. 10 is a cross-sectional view taken along the line Z-Z in FIG. 1;

[0044]FIG. 11 is an enlarged partial view of the B part in FIG. 2;

[0045]FIG. 12 is a whole scheme diagram, which shows a conventional plastic liquefying device;

[0046]FIG. 13 is an enlarged partial view of the conventional plastic liquefying device's gasifying device;

[0047]FIG. 14 is a longitudinal sectional view, which shows another embodiment of the gasifying furnace in the present invention;

[0048]FIG. 15 is a cross-sectional view taken along the line A-A in FIG. 14;

[0049]FIG. 16 is a graph, which shows the relationship between the temperature and the pressure inside of the gasifying furnace shown in FIG. 14;

[0050]FIG. 17 is a whole scheme diagram, which shows an embodiment of the plastic liquefying device as it is in the present invention; and

[0051]FIG. 18 is a cross-sectional view taken along the line A-A in FIG. 17.

BEST MODE FOR CARRYING OUT THE INVENTION

[0052] Hereinafter, the best mode of the present invention will be described in reference to the accompanying drawings.

[0053]FIG. 1 is a longitudinal sectional view, which shows an embodiment of gasifying furnace 19, which is a part of the plastic liquefying device in the present invention. FIG. 2 is a cross-sectional view taken along the line X-X in FIG. 1.

[0054] As shown in the drawings, the gasifying furnace 19 comprises an oven-shaped furnace body including a plastic wastes inlet H, an opening and closing mechanism 21 for opening and closing the inlet H, and a heating means for heating the furnace body from its exterior. The furnace body has a structure which is covered with an insulative casing 23.

[0055] The furnace body 20 is made of a metal such as hastelloy, stainless-steel or superalloy which has an excellent heat resistance, corrosion resistance, and heat conductivity effect. The plastic wastes which are loaded from the inlet H are melted by the heating means 22 and pyrolytically decomposed. The pyrolytic gas is supplied sequentially into the above-mentioned liquefying tank from a gas outlet 20 a.

[0056] The opening and closing mechanism 21 includes a plate shutter 24 for opening and closing the plastic wastes inlet H and a locking means 25 for locking the shutter 24 by pressing the shutter 24 onto sealing surface S which is formed around the peripheral edge of the inlet H.

[0057] As shown in FIG. 3 and FIG. 4, the shutter 24 has a similar shape to the inlet H which opens in a rectangle shape. The shutter is made of a heat resistant rectangle plate, which is sufficiently larger than the aperture area of the inlet H. In addition, the both side of the shutter includes two pairs of wheels 26, 26, 26, 26 (4 wheels in total) (either one or two pairs). Since these wheels run along a pair of rails 27 and 27 which extend horizontally from both sides of the inlet H, the shutter is horizontally moved by a sliding motion to the inlet H. Also, both side ends of the shutter 24 integrally include brackets 28 and 28 which extend in an orthogonal direction to the shutter's movable direction, and the inlet H is opened and closed by sliding the shutter 24 in a horizontal direction by way of a sliding means, which includes a pair of hydraulic cylinders 29 and 29. That is to say, both one end of each hydraulic cylinder 29 is fixed to a bracket 28 of the shutter 24 while the other side is fixed to the bracket 30 of an inlet casing 23 a. Consequently, as shown in FIG. 4, by simultaneously expanding and contracting the hydraulic cylinders 29 and 29 from brackets 30 and 30 which are starting points, the shutter 24 is controlled to be easily opened and closed.

[0058] As shown in FIG. 1 and FIG. 2, the locking means 25 includes totally four hydraulic cylinders 31 which each pair of which is provided at back and forth respectively and vertically supported on the upper part of the inlet casing 23 a, and channel shape presser claws 32, which are provided at the each corner of shutter 24. When the shutter 24 is closed, each presser claw 32 and each cylinder rod 33 of each hydraulic cylinder 31 are engaged with each other. Thus, the shutter 24 is secured by engaging the presser claws 32 to the piston rods 33 so that the inlet H is completely closed.

[0059] As shown in FIG. 5 to FIG. 8, each of cylinder rods 33, 33, 33, 33 includes circular plate shape collars 34. After the presser claws 32 are fitted with piston rods 33, the cylinder rods 33 are extended and their collar parts 34 forcibly press presser claws 32 down. Accordingly, the shutter 24 is pressed onto the sealing surface S at each of four collar parts. After closing the inlet H completely by the shutter 24, pulling the cylinder rods 33 in an upper direction results in easy unlocking of the shutter 24 to resume a sliding.

[0060] When the shutter 24 is pressed forcibly down to the inlet H, and the rails 27 and 27 which support the shutter 24 are fixed, the vertical movement of the shutter 24 is limited by the wheels 26. Therefore, as shown in FIG. 1 and FIG. 3, in the present embodiment, the rails 27 and 27 are divided into two parts in a longitudinal direction. As shown in FIG. 5 and other drawings, the divided rail segments 27 a and 27 a which are arranged at the side of the inlet H are supported by a coiled spring 35 to be able to move in a vertical direction. As shown in FIG. 6, the rail segments 27 a and 27 a is movable in the up and down directions with the shutter 24, so that the vertical movement of the shutter 24 is not limited. In addition, as shown in FIG. 5, the end of rail segments 27 a and 27 a are connected with H-shape connecting beam 36. The cylinder rods 33 may further include another collar part 37 connecting with the connecting beam 36, so that the divided rails 27 a and 27 a are simultaneously movable with the vertical movement of the cylinder rods 33.

[0061] As shown in FIG. 11, at the peripheral edge of the inlet H of the furnace body 20, a purge gas header 38 is extends along the perimeter of the peripheral edge. By spraying the purge gas supplied from the purge gas tank or the like (not shown) onto the sealing surface of the inlet H through a slit which opens at the upper part of the purge gas tank, even if a part of plastic wastes and dirt are adhered or accumulated on the sealing surface H, it is possible to remove them from the sealing surface S by the pressure of the purge gas. A slit 39 includes a guide piece 40 to guide the purge gas into the direction of sealing surface H. The guide piece 40 is made of a flexible blade spring. When the shutter 24 is opened or closed, the guide piece 40 is easily deflected, so that there is no interference with the shutter 24.

[0062] As shown in FIG. 1, FIG. 2 and FIG. 10, the bottom part of the furnace body 20 forms a corrugated shape by having a plurality of canaliculate shape members 20 b, 20 b . . . in parallel to each other. The each end of the canaliculate shape members 20 b, 20 b . . . includes a similar canaliculate shape discharge pipe 20C to merge extending herefrom. The bottom area of the furnace body is larger than a flat plate bottom. In particular, it is about ½π rtimes larger than the flat plate bottom area.

[0063] Further, the inside of each of the canaliculate shape members 20 b, 20 b . . . and the discharge pipe 20 c coaxially include rotatable screw conveyers 41, 41 . . . which extend in a longitudinal direction, so that the insolubles accumulated at the bottom of the furnace, such as dirt, metal scrape, a glass, or sludge, are forcibly scraped from the bottom wall of the furnace and discharged from the discharge opening 42 which is formed on the casing 23 through canaliculate member 20 b, 20 b . . . to the discharge pipe 20 c. The discharge opening 42 includes an opening and closing valve (not shown). Of course, the valve is closed while in operation in order not to leak any melting liquid or give off any pyrolytic gas from the discharge opening 42 to the outside.

[0064] Each end of rotation axis of the screw conveyers 41,41 . . . which are provided in the canaliculate shape members 20 b, 20 b . . . penetrates casing 23 and extends to the outside respectively. Each end of the axis of the screw conveyers 41 further includes pulleys 43, 43 . . . respectively. By connecting each pulley 43 to a scraping motor 44 which is fixed to the outside of the casing, with a belt 45, the screw conveyers 41,41 . . . can be rotated simultaneously in the same direction.

[0065] The end of rotation axis of the screw conveyer 41 which is located in the side of the discharge pipe 20 c, also penetrates the casing 23 and extends to the outside. The screw conveyer is rotated by connecting the pulley 46 located at the end of the screw conveyer to a discharge motor 47 with a belt 48.

[0066] As shown in FIG. 11, reinforcing plates 49,49 . . . which are band plate shapes, and extend in an elongated direction are provided among the canaliculate shape members 20 b, 20 b . . . . A metal heat gauge 50 is embedded in the reinforcing plate 49. The strength of the bottom furnace is maintained by these reinforcing plates 49, 49 . . . . The temperature of the bottom furnace can be measured at any time by the metal heat gauge 50. In addition, the temperature information read on the metal heat gauge 50 is input into the control unit which controls output from a gas burner which will be described hereinbelow.

[0067] As shown in FIG. 1 and FIG. 2, a heating means 22 for heating the furnace body 20 includes a combustion chamber 51 which is located at the bottom of the furnace body 20, a gas burner 52 which is provided in the combustion chamber 51 and a jacket 53 which covers around the furnace body 20 while maintaining a certain distance from it. The furnace body 20 can be heated from its bottom part by combustion gas generated in the combustion chamber 51 by the gas burner 52. The exhaust combustion gas is guided into the jacket 53 which is communicated with the combustion chamber 51 and further guided to the outside from an exhaust gas exit 54 which is located at the top part of the jacket 53. Because of this structure, the furnace body 20 can be heated from its lateral side and its surroundings.

[0068] The present embodiment further includes parting strips 55 which spirally separate the inside of the jacket 53. The high temperature exhaust combustion gas which is guided into the jacket 53 is not directly flown into the gas exit 54, but the gas is spirally flown around the furnace body 20 by the parting strips 55. Consequently, it makes it possible to cause the longest contact between the high temperature exhaust combustion gas and the furnace body 20. As shown in FIG. 1 and FIG. 2, the reference numeral 56 denotes a maintenance hatch for opening and closing the combustion chamber, and the reference numeral 57 denotes its opening and closing lid. The reference numerals 58 and 58 denote supporting legs for the furnace body. The reference numeral 59 denotes a hopper to facilitate the loading of the plastic wastes. The reference numeral 60 denotes a view port for checking the inside of the combustion chamber 51.

[0069] In the gasifying furnace 19 of the present invention which has the above-described structure, the shutter 24 which closes the inlet H of the furnace body 20 is closed in such as that the shutter 24 is pressed to the sealing surface S of the inlet H by way of hydraulic cylinders 31, presser claws 32 and the like. Therefore, even if the inside of the pressure of the furnace body 20 is raised during its operation, the gap between the shutter 24 and the sealing surface S can not be compromised. Accordingly, inconveniences such as contaminating the surrounding environment because of harmful pyrolytic gas leaks can certainly be prevented.

[0070] In addition, the peripheral edge of the inlet H includes a purge gas header 38. When the shutter 24 is closed, the high pressure purge gas is sprayed onto the sealing surface S from the purge gas header 38 in order to certainly remove the part of the plastic wastes and dirt from the sealing surface, which may be attached when the plastic wastes are placed. Therefore, it is certainly avoided to compromise the gap on the sealing surface because of the attachment of the dirt, or the like.

[0071] The surface of the bottom of the furnace body 20 is enlarged by forming a corrugated surface at the bottom of the furnace body 20 with a plurality of canaliculate shape members 20 b, so that the contact surface between the high temperature generated combustion gas and the bottom of the furnace is enlarged. Consequently, the heating efficiency of the furnace body 20 is improved and efficient melting or pyrolytic decomposition can be achieved. Moreover, the screw conveyers 41 are provided in the canaliculate shape member 20 b or the like, so that solids, sludge, or the like which has accumulated or attached to the bottom of the furnace are scraped from the bottom of the furnace and are easily removed. Accordingly, there is no need to remove them by hand, which was previously burdensome work in the conventional device. Also, the removal can be done even when the furnace body maintains a high temperature, so that the down time of the furnace body is curtailed and a high operating rate can be maintained.

[0072] The metal heat gauge 50 for measuring the temperature of the bottom of the surface is provided at the bottom of the furnace, so that it is possible to accurately measure the temperature of the whole furnace body 20 together with a conventional furnace body heat gauge. For example, when the temperature gap between the temperature of the bottom of the furnace measured by the metal heat gauge 50 and the temperature of the inside of the furnace body 20 measured by the furnace body heat gauge is small, it can be determined that the gasifying process has not finished and the operation should be maintained. On the other hand, when the temperature gap exceeds a predetermined value, it can be determined that the gasifying process has finished.

[0073] In the operating method of the plastic wastes furnace according to the present embodiment, it is necessary to add some water at the same time or about the time when the plastic wastes are loaded at its initial operation stage, which is same as in the above-mentioned conventional device. However, because of the corrugated shape of the furnace bottom, the contact surface between the loaded plastic wastes and the bottom of the furnace (furnace wall) is decreased. Consequently, in the initial operation stage, there is a possibility that the heat transmission (melting) cannot be performed under the best conditions. For example, if a small amount of high boiling oil such as reclaimed oil is added with the water, following the water evaporation, the high boiling oil evaporation could be carried out. Accordingly, even if the contact surface between the plastic wastes and the heat transmission surface (furnace wall) is small, the heat transmission can be efficiently carried out, and effective melting can be accomplished.

[0074]FIG. 14 is a longitudinal sectional view which shows an embodiment of another gasifying furnace 60 for gasifying the infectious plastic wastes which especially have a possibility of the attachment of the infectious bacteria pathogen in injectors or the like compared with the above-mentioned plastic wastes. FIG. 15 is a cross-sectional view taken along the line A-A in FIG. 14.

[0075] As shown in the drawings, the gasifying furnace 60 mainly includes an elongated tube shape furnace body 61 for pyrolitically decomposing infectious plastic wastes and generating pyrolytic gas, a heating means 62 for heating the furnace body 61 from its bottom and an agitating means 63 for mixing the inside of the furnace body 61.

[0076] The furnace body 61 is made of a metal such as hastelloy, stainless-steel or superalloy which has an excellent heat resistance, corrosion resistance, and heat conductivity effect. The furnace body 61 is a pressure vessel, in which top and bottom of a longitudinal tube shape sack body 64 respectively include hemispheric end covers 65 and 66. An inlet 67 for the placement of the plastic wastes is provided at the top end cover 65. Moreover, the inlet 67 can be opened and closed by the flanged type opening and closing lid 68. The inlet 67 is connected to the feed water pipe 69 for feeding water to promote melting in the initial stage. The feed water pipe 69 can be opened and closed by a magnetic valve V.

[0077] A gas outlet 70 is provided at the upper part of the sack body 64, and pyrolytic gas which is generated by the furnace body 61 can be guided into the above-mentioned liquefying tank 2. Moreover, the gas outlet 70 also includes an automatic opening and closing valve 71 and the gas outlet 70 can be automatically opened and closed by a predetermined condition which is mentioned below.

[0078] The bottom end cover 66 of the furnace body 61 includes an insoluble vent 72 for removing insolubles such as sand or metal pieces, which have accumulated at the furnace bottom, as needed.

[0079] The heating means 62 includes a combustion chamber 73 located at the bottom of the furnace body and jacket 74 which covers the surrounding area of the furnace body 61 from the combustion chamber 73. A heating device 75 located in the combustion chamber 73, such as a gas burner, an oil burner or an electrical heater, directly heats the furnace body 61 from its bottom. When the gas burner, the oil burner or the like which utilizes fossil fuel is employed as the heating device 75, the high temperature of combustion gas generated in the combustion chamber 73 is guided into the exhaust gas outlet 76 through jacket 74. Accordingly, the furnace body can be heated evenly over its entire body.

[0080] An agitator 63 located in the furnace body 61 includes a drive shaft 77 which is positioned in the shaft center part of the furnace body 61, a driving motor 78 which is installed at the upper part of the drive shaft 77 to rotatably drive the drive shaft 77, and a plurality of moving vanes 79, 79, 79, 79 which radially extend from the bottom part of the drive shaft 77, to efficiently melt the infectious plastic wastes loaded in the inside of the furnace body 61 by mixing and heating the wastes evenly. As shown in FIG. 2, the tips of the moving vanes 79, 79, 79, 79 are curved toward the down stream side of the rotative direction, and the bottoms of the moving vanes 79 are normally in contact with the bottom of the furnace. When the moving vanes revolve and slide on the bottom surface like scraper, the attachment and accumulation of stickum, insolubles or the like to the bottom of the furnace can be prevented.

[0081] One example of the operation method for the gasifying furnace 60, which has the above-mentioned structure of is described below.

[0082] Firstly, as shown in FIG. 14, after an inlet 67 positioned at the top of the furnace body 61 is opened, infectious plastic wastes and a small amount of water are loaded into the inside of the furnace body 61. Then, an automatic opening and closing valve 71 of a gas outlet 70 and a valve V of the water feed pipe 69 are closed. In other words, the furnace body 61 is hermetically closed, and the furnace body 61 can be heated by the heating means 62 with driving an agitator 63.

[0083] In the furnace body 61, firstly water which has a lower boiling point starts evaporating by the heating mentioned above. Following to the evaporation, the pressure and the temperature inside the furnace body are gradually raised, as shown in FIG. 16. The heating means 62 is adjusted as needed to keep the pressure or temperature which eradicates infectious bacterial pathogen, for example, as shown in FIG. 16, the saturation pressure can be established at 121° C. water temperature, and the condition is maintained for a predetermined time of period, twenty minutes, for example. Then, the infectious bacterial pathogen which is attached to the plastic wastes is completely eradicated by steam sterilization un der pressure. Therefore, there is no possibility that the infectious bacterial pathogen flows into the liquefying tank 2 together with pyrolytic gas.

[0084] Thus, after meeting the condition in which the infectious bacterial pathogen is completely sterilized, as shown in FIG. 16, the inside pressure of the furnace body 61 can be decreased by gradually opening the automatic opening and closing valve 71 of the gas outlet 70. At the same time, the inside temperature is raised by increasing the energy output of the heating means. In the furnace body 61, following the evaporation of the water which has placed at the first stage of the operation, plastic wastes start melting. Also, the temperature is increased, and when the temperature reaches the gasifying temperature, for example 380° C., the melt liquid is pyrolitically decomposed and gasified. The pyrolytic gas is sequentially guided into the liquefying tank 2, and then the oily water separation, which is conducted in the same way as the conventional process, is undertaken. Such reclaimed oil or the like can be effectively utilized.

[0085] In the gasifying furnace 60 according to the present embodiment, it is possible that the furnace body 61 can be hermetically closed with high pressure and under high temperature for a certain period of time, so that the infectious plastic wastes such as injectors or catheters for infectious disease, in which the infectious bacterial pathogen is attached, can be pyrolitically decomposed of safely and surely.

[0086] After all the plastic wastes loaded inside the gasifying furnace 60 has pyrolitically decomposed, the same disposal process can be repeated by butch processing. However, in cases of metal pieces such as injector needles or insolubles (solid) such as dirt which have gradually accumulated inside the furnace body during pyrolytic decomposition, the insolubles disposal exit 72 at the bottom of the furnace body 61 can be opened, and the insolubles can be easily removed by revolving the moving vanes 79 of the agitating means 63. Accordingly, disadvantages such as the deterioration of the heat transmission and the decrement of the furnace capacity, which are caused by the attachment and accumulation of the insolubles at the furnace bottom, are easily eliminated.

[0087]FIG. 17 and FIG. 18 show other embodiments of the plastic liquefying device according to the present invention.

[0088] As shown in the drawings, this plastic liquefying device mainly comprises a gasifying furnace 80 for melting plastic wastes, generating pyrolytic gas and a liquefying tank 81 for condensing and separating the pyrolytic gas which is generated in the gasifying furnace 80, similar to the conventional device.

[0089] Firstly, as shown in FIG. 1 and FIG. 2, the gasifying furnace 80 comprises a heating means 83 for heating a furnace body 82 from its exterior. The heating means is located in the furnace body 82 having an inlet H at its upper part. The variety of mixed plastic wastes (which are limited to the thermoplastics) which are loaded from the inlet H, are melted by the heating means 83, and gasified. The pyrolytic gas is guided into the liquefying tank 81 through a gas line G1 from a gas outlet 84.

[0090] A closure lid 85 is connected to the end of the inlet H located at the furnace body 82 by way of hinges. The closure lid 85 is arbitrarily opened and closed by an opening and closing member 86 such as a motor cylinder, which is positioned between the bottom surface of the closure lid and the wall of the inside furnace body 82.

[0091] The bottom of the furnace body 82 curves into a valley shape toward its center. A screw conveyer 87 which extends in a horizontal direction is provided at the bottom part of the valley shape. As shown in FIG. 2, the screw conveyer 87 integrally includes a spiral screw 89 around a rotation axis 88 which extends along an elongated direction of the bottom part of the valley shape. One end of the rotation axis 88 penetrates the furnace body 82 and connects to a driving motor 90 which is located outside, so that the axis of rotation 88 revolves in both directions by the driving motor 90. The other end of the rotation axis 88 includes a discharge opening 91. The discharge opening 91, which can be opened and closed, is closed by an exhaust lid 92.

[0092] As shown in FIG. 1, the heating means 83 for heating furnace body 82 includes three flat shape heaters 93, 94, 95. The flat shape heater 94 is located at the bottom of the furnace body 22, and the flat shape heaters 93 and 95 are located at the both sides of the bottom part, and independently operate.

[0093] The liquefying tank 81 liquefies the pyrolytic gas which is guided from the gas line G1 and stores the pyrolytic gas temporarily. A landscape tank 96 includes a jet scrubber 97 which sprays cooling water onto the pyrolytic gas guided from the gas line G1 and condenses it, and a cleaning column 98 which cleans and exhausts unliquefied gas which has not liquefied by the jet scrubber 97.

[0094] The bottom of the water tank 96 narrows into a funnel-like shape. The rock bottom part is connected to a drain line L1 through a valve V1 and the middle part is connected to an oil recovery line L2 through a valve V2.

[0095] This drain line L1 includes a strainer 99 and a circulating pump 100. The drain line L1 extracts water from the water tank 96, circulates the water to the above-mentioned jet scrubber 97 and the cleaning column 98, and also returns a part of the water to the above-mentioned gasifying furnace 80 through a return line L3. In addition, the return line L3 and its branch part include lines L1, L3, a scrubber line L4 and magnetic valves V3, V4, V5, V6 which respectively open and close the cleaning column line L5.

[0096] Also, the drain line L1 is connected to a neutralization tank 101 via a branch line L6 and a valve V7, and the water extracted from tank 96 is neutralized by injecting the neutralizer. A cooling water line L9 and valve V9 branch off from the scrubber line L4, and cooling water (tap water) is supplied to the jet scrubber 97. Furthermore, the oil recovery line L2 includes a reclaimed oil tank 102, and the reclaimed oil, which was separated in the water tank 96, is extracted from the oil recovery line L2 and stored.

[0097] A cleaning column 98 includes an upper spray nozzle 104, a demister 105, a lower spray nozzle 106 and a baffle plate 107 in orders from the top in the vertical column body 103. The pyrolytic gas, which has not been liquefied by the lavation (tap water, etc.) that flows from a cleaning column line L5 and a cooling water line L10, is cleaned and then sent to the exhaust line L7. Also, the exhaust line L7 includes a pre-heater 108 and a catalytic deodorizer 109, so that the gas is pre-heated and deodorized, and then is released to the atmosphere.

[0098] In the drawings, the reference numeral 110 denotes a level meter for measuring liquid level in the water tank and the reference numeral 111 denotes a translucent liquid level meter for checking the condition of the oily-water separation from the outside. Also, the reference numeral 112 denotes a heat insulating material for preventing the gas line G1 which extends between the gasifying furnace 80 and the liquefying tank 81 from cooling down.

[0099] Next, the operation of the plastic liquefying device according to the present embodiment, which has above-mentioned structure, that is to say, the disposal process of the plastic wastes is described hereinafter.

[0100] Firstly, in the disposal process of plastic wastes, before loading the plastic wastes into the gasifying furnace 80, a small amount of water is put into the furnace body 82 of the gasifying furnace 80. Then the opening and closing lid 85 is closed, and the furnace body 82 is heated with a condition in which the inside furnace body 82 is hermetically closed. In this initial stage, there is no need to operate all flat shape heaters 93, 94, 95 of the heating means 83, so that only one of the heaters, for example, the bottom part heater 94 is operated.

[0101] The water placed into the inside of the furnace body 82 evaporates into steam by the heat, and then flows into the liquefying tank 81 through the gas line G1 from the gas outlet 84. Furthermore, the steam flows into the drain line L1, the oil recovery line L2, and the exhaust line L7, etc. from the liquefying tank 81. Accordingly, the steam expels all the air inside the device.

[0102] Thus, when the inside of the device is replaced with steam, the valve V1 of the drain line L1 connected to the liquefying tank 81 and the valve V2 of the oil recovery line are closed. Then, the opening and closing lid 85 of the gasifying furnace 80 is opened again, and the plastic wastes to be disposed are loaded into the furnace body 82 from the inlet H. After the furnace body 82 is hermetically closed by closing the lid 85 again, the furnace body 82 is heated by the heating means 83.

[0103] After melting and liquefying the plastic wastes which are loaded in the furnace body 82 by the heating means, the pyrolytic gas which is sequentially and pyrolitically decomposed, flows from the gas outlet 84 to the gas line G1, then reaches the jet scrubber 97 of the liquefying tank 81. At this time, as shown in FIG. 18, the opening and closing lid 85 is secured to the furnace body 82 by bolts B or the like, so that the inside of the furnace body is hermetically closed. Accordingly, the pyrolytic gas leak is completely prevented and the above-mentioned infectious plastic wastes such as injectors are safely disposed of.

[0104] After that, the pyrolytic gas which has reached the jet scrubber 97, is contacted with cooling water supplied from the drain line L1 and the branch line L4 to cause a vapor-liquid contact, and then the pyrolitic gas is rapidly cooled down and liquefied into reclaimed oil. The reclaimed oil is sequentially stored into the water tank 96 together with the cooling water. When the screw conveyer 97 is revolved, and the inside of the furnace is agitated, the melting process of plastic wastes in the gasifying furnace 80 is efficiently accomplished. Also, the pyrolytic gas is cooled down by way of the jet scrubber 97, so that terephtalic acids or the like which directly solidifies from the gas, is not clogged. Thus, it is possible to maintain the efficient gas circulation. If the jet scrubber is substituted by for example, a fin-tube heat exchanger, such terephtalic acid which directly solidifies from the gas, is generated inside the tube, and may cause blockages by the accumulation of the solid. Even if the gas is solidified around the exit, the solid can be blown off by the jet water of the jet scrubber 97. Thus, disadvantages such as blockage are not caused.

[0105] On the other hand, un-liquefied gas (pyrolytic gas), which could not be liquefied by the jet scrubber 97, passes though the upper space of the water tank 96 as it is and after being cleaned by the cleaning column 98 and also deodorized and purified by the exhaust gas line L7, the pyrolytic gas exhausts into the atmosphere.

[0106] Thus, when all the plastic wastes loaded into the gasifying furnace 80 have been gasified into the pyrolytic gas and have flown into the liquefying tank 81, the heating of the furnace body 82 is stopped. At this time, however, if the loaded plastic wastes include insolubles such as dirt, metal pieces or timber pieces, they accumulate at the furnace bottom, and cause the decrement of the furnace cap acity and the deterioration of the heat transmission from the heating means 83. Accordingly, when such insolules are accumulated to some degree, as shown in FIG. 18, a lid 92 of a discharge opening 91 at the furnace bottom and the screw conveyer 87 are driven. Accordingly, the accumulated insolubles are carried to the discharge opening 91 and easily disposed of through the discharge opening 91. Thus, the furnace body cleaning which is done by workers at the conventional device is no longer needed.

[0107] The mixed liquid of cooling water and reclaimed oil, which is stored in the water tank 96 of the liquefying tank 81, is separated by its own specific gravity after setting for a while. In other words, the reclaimed oil which has a light specific gravity can be collected to the liquid surface, and water which has a heavy specific gravity is collected at the bottom part. Firstly, the valve V2 of the reclaimed oil line L2 is opened, and the reclaimed oil at the upper part flows into the reclaimed oil tank 102, so that only reclaimed oil can be efficiently collected by the separate collection. After a certain amount of the reclaimed oil has been removed, the water can be extracted from the bottom through the drain line L1, which are then recycled as cooling water for the next process. However, as illustrated, if any substances such as solid terephtalic acid which specific gravity is heavier than that of water or oil is contained, it is accumulated in layers at the bottom of the tank. Therefore, when recycling the water in the water tank, the constituents which have heavier specific gravity, need to be previously extracted by the exhaust oil line L8 which branches off from the upper part of the drain line L1. Then, only the substances which have a heavier specific gravity can be collected. Also, the water in the water tank can be recycled as cooling water for the water used at the initial operation and also as cooling water for the jet scrubber 97 as was mentioned above. Therefore, the effective utilization of the resource can be accomplished. If the extracted water includes chlorine or the like, it may incur acid corrosion of the pipes in each line. Therefore, the water is neutralized by adding an adequate dose of the neutralizer such as caustic soda. The water can be then recycled.

[0108] When the collection of the reclaimed oil is completed, new plastic wastes can be added, and the process, such as the above-mentioned heating and gasifying decomposition is carried out by batch processing. Thus, regardless of its composition, the majority of the plastic wastes can be efficiently disposed of and the effective utilization of resources can be accomplished.

[0109] The present embodiment employs the electrical flat shaped heaters 93, 94, 95 as the heating means 83 of the gasifying furnace 80. However, a gas burner or the like may be alternatively used. 

What is claimed is:
 1. A plastic liquefying device comprising a gasifying furnace for generating pyrolytic gas by melting plastic wastes; and a liquefying tank for liquefying and separating the pyrolytic gas generated at the gasifying furnace, wherein the gasifying furnace comprises: heating means located at a bottom of an oven-shaped body of the furnace for heating an inside of the furnace, an oven-shaped body of the furnace having a plastic waste inlet at an upper part thereof; and an opening and closing mechanism located at the inlet for opening and closing the inlet, wherein the opening and closing mechanism comprises: a plate shutter at least larger than an aperture area of the inlet; and locking means for securing the shutter onto a sealing surface of the inlet peripheral edge by way of pressure.
 2. A plastic liquefying device of claim 1, wherein sliding means for opening and closing the inlet by horizontally sliding the shutter is provided at the shutter.
 3. A plastic liquefying device of claim 1, wherein the sliding means is a hydraulic cylinder with one end connected to the shutter and the other end pivotably connected to the furnace body.
 4. A plastic liquefying device of claim 1, wherein the locking means is a hydraulic cylinder which secures the shutter onto the sealing surface by way of pressure from above.
 5. A plastic liquefying device of claim 1, wherein a purge gas header which sprays purge gas onto the sealing surface is provided at the peripheral edge of the inlet.
 6. A plastic liquefying device of claim 1, wherein a corrugated surface which is formed by a plurality of canaliculate members placed parallel to each other is provided at a bottom of the furnace body.
 7. A plastic liquefying device of claim 6, wherein a canaliculate-shape discharge pipe is provided such that the discharge pipe merges with ends of the canaliculate member, and a screw conveyer is provided in each of the canaliculate members and the discharge pipe.
 8. A plastic liquefying device of claim 1, wherein the heating means comprises a gas burner, a jacket which covers a perimeter of the furnace body to flow exhaust combustion gas from the gas burner, and a parting strip which is arranged spirally at the jacket.
 9. A plastic liquefying device comprising a gasifying furnace for generating pyrolytic gas by melting plastic wastes and a liquefying tank for liquefying and separating the pyrolytic gas generated at the gasifying furnace, wherein the gasifying furnace comprises: a vertical tube body for receiving infectious plastic wastes, heating means for heating the vertical tube body from its surrounding and generating pyrolytic gas by pyrolitically decomposing infectious plastic wastes, and an agitator to agitate an inside of the furnace body, wherein the top part of the furnace comprises: an inlet to receive the infectious plastic wastes, an opening and closing lid for opening and closing the inlet, a gas outlet for exhausting the pyrolytic gas, and the gas outlet includes an automatic opening and closing valve.
 10. A plastic liquefying device of claim 9, wherein the furnace body is a pressure vessel, the furnace body has a vertical tube shape metal sack body, the hemispheric end covers are provided at both top and bottom parts thereof, and an opening and closing lid and the gas outlet are further provided at the top part.
 11. A plastic liquefying device of claim 9, wherein the agitator comprises a drive shaft which is positioned at a shaft center part of the furnace body, a driving motor for rotating the drive shaft, and a plurality of moving vanes which radially extend from the drive shaft, and the moving vanes respectively revolve in contact with the bottom of the furnace.
 12. A plastic liquefying device of claim 9, wherein a discharge opening for discharging insolubles is provided at the bottom part of the furnace body.
 13. A plastic liquefying device comprising a gasifying furnace for heating various kinds of plastic wastes and generating pyrolytic gas and a liquefying tank for condensing the pyrolytic gas generated at the gasifying furnace and then separating, wherein the bottom part of the gasifying furnace narrows in a valley-shape and includes a screw conveyer and an outlet for discharging insolubles.
 14. A plastic liquefying device of claim 13, wherein the liquefying tank includes a jet scrubber for spraying a cooling water onto the pyrolytic gas to condense the pyrolytic gas, and a cleaning column for cleaning exhaust gas in a landscape water tank, the bottom part of the water tank narrows in a funnel-shape and is connected to a drain line, and a middle part of the water tank is connected to an oil recovery line.
 15. A plastic liquefying device of claim 14, wherein a neutralization tank for infusing neutralizer is provided at the drain line. 